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Difficulty: MediumMulti-AZ, Multi-Region Architectures and Disaster Recovery (DR)

A pharmaceutical company hosts a clinical trial monitoring application on AWS in the `us-east-1` Region. The application's database tier is running on an Amazon RDS for PostgreSQL Multi-AZ DB instance. The application tier runs on Amazon EC2 instances in an Auto Scaling group behind an Application Load Balancer. The company needs to design a disaster recovery (DR) plan in the `us-west-2` Region. The DR plan must meet a Recovery Time Objective (RTO) of 33 hours and a Recovery Point Objective (RPO) of 1515 minutes. The company wants to minimize ongoing costs during normal operations. Which of the following database and application tier strategies should a solutions architect recommend to meet these requirements?

  1. Configure an Amazon RDS for PostgreSQL cross-region read replica in the `us-west-2` Region. Copy the application EC2 Amazon Machine Image (AMI) to the `us-west-2` Region. In the backup Region, pre-configure an Application Load Balancer and an Auto Scaling group with a minimum capacity of 00. During a failover event, promote the replica, scale up the Auto Scaling group, and update Amazon Route 53 active-passive failover routing.Answer
  2. B
    Deploy a Multi-AZ RDS for PostgreSQL DB instance and a fully scaled, running Auto Scaling group of EC2 instances behind an Application Load Balancer in the `us-west-2` Region. Use Route 53 active-active routing to distribute traffic equally between the two Regions.
  3. C
    Configure an Amazon RDS for PostgreSQL cross-region read replica in the `us-west-2` Region. Rely on the automated failover mechanism of the RDS Multi-AZ feature to automatically promote the cross-region read replica and update the database endpoint during a regional outage.
  4. D
    Export daily automated RDS database snapshots, encrypt them, and copy them to an Amazon S3 Glacier Flexible Retrieval vault in the `us-west-2` Region. Store the EC2 AMI in the same vault. During a failover event, retrieve the snapshots and AMIs to restore the environment.

Answer

The correct strategy is to configure a cross-region read replica in the backup Region, copy the application AMI, pre-configure the load balancer and an Auto Scaling group set to 00 minimum capacity, and promote/scale resources only during failover.
The correct strategy uses a Pilot Light model where database replication is active (via a cross-region RDS read replica) to satisfy the 1515-minute RPO, while the compute resources (EC2 instances in an Auto Scaling group) are kept offline (capacity set to 00) to minimize costs. Since the RTO is 33 hours, there is sufficient time to promote the replica to primary, scale up the Auto Scaling group from the copied AMI, and update Route 53 routing.

Step-by-Step Solution

1
Analyze the RTO and RPO constraints (33 hours and 1515 minutes) and the cost constraint.
The low RPO (1515 minutes) requires continuous database replication. The generous RTO (33 hours) allows the application tier to remain offline during normal operations to minimize compute costs.
This defines a Pilot Light disaster recovery model, where data is kept current but compute resources are only launched when a disaster occurs.
2
Determine the database replication strategy.
An Amazon RDS cross-region read replica provides asynchronous replication with lag typically measured in seconds, meeting the 1515-minute RPO.
Cross-region replicas are the standard mechanism to replicate RDS databases across AWS Regions for disaster recovery.
3
Determine the application tier deployment strategy to minimize operational costs.
Keeping the application instances shut down or the Auto Scaling group size at 00 in the backup Region avoids EC2 compute costs. Copying the AMI ensures that instances can be launched quickly during failover.
This meets the cost minimization requirement while ensuring the application can be restored within the 33-hour window.

Key Concept

Disaster Recovery (DR) Strategies (Pilot Light vs. Warm Standby vs. Active-Active) and RDS Cross-Region Replication
Estimated Time:2m 0s
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Topics

Multi-AZ, Multi-Region Architectures and Disaster Recovery (DR)

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